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Load sensing proves its mettle

Steaks were once considered the biggest export of Argentinean agriculture. Now, its number one export is corn — 80 million tonnes annually from 1.8 billion km 2 of farm land. Not surprisingly, Argentina needs a lot of tractors. The 500 GLP, from Pauny S.A., Buenos Aires, became the first tractor manufactured in Argentina to take full advantage of hydraulic load-sensing technology. Powered by liquid natural gas, which costs about half that of diesel fuel in Argentina, the tractor originally used a fixed-displacement pump to power its hydraulic system. Following a restructuring in 2002, Pauny began building 120-to 300-hp tractors in 2002, and later looked to Bosch Rexroth to help them improve the hydraulic system.

A variable-displacement pump and load-sensing hydraulics give this tractor more power at the wheel — which translates to higher productivity — and lower power consumption at idle, which means higher fuel efficiency.

Because it used a fixed-displacement pump, the original tractor could not respond to changes in load demand. Consequently, unused power was converted to heat, which wasted fuel when the tractor was idling because the hydraulic pump placed a substantial load on the engine even though no work was being performed. In addition, productivity suffered when the pump could not deliver enough power to the wheels to serve peak demand.

Omar Perez, design manager at Pauny, explained that the load-sensing solution using a variable-displacement pump boosts output power by 15 to 20 hp. Because the new hydraulic system delivers more power to the wheels, the 500 GLP can now handle larger attachments. For example, with the old design, farmers were limited to using sowing machines with a working width of 12.6 m covering 18 furrows. Now, the tractor can pull 14-m wide sowing machines covering 20 furrows.

The tractor also consumes much less fuel. When the tractor is idling, the A10V0 size 45 axial-piston pump shifts to near zero stroke, drastically reducing the load imposed on the engine. The new 500 GLP tractor also uses an SB23LS control block containing three directional control valves. This circuit adjusts pressure and flow to one or more actuators to match hydraulic power to load requirements. As a result, the redesigned tractor not only uses less fuel, but boasts higher productivity as well.